Haiti descended into lawlessness last night as machete-wielding looters marauded streets in a frantic hunt for food.

Gangs of starving survivors – many without food or water since Tuesday’s disaster – ransacked shops and UN depots.

The chaos in devastated capital Port-au-Prince is a sign of Haitians’ mounting desperation as quake damage and the country’s ramshackle airport hinder efforts to rush aid to three million victims.

UN spokeswoman Elisabeth Byrs said: “People have not been eating or drinking for almost 50 hours and are already in a very poor situation.

“If they see a truck with something or see a supermarket that has collapsed, they just rush to get something to eat.”

Emilia Casella, spokeswoman for the UN’s World Food Program, added: “Stores have been cleaned out. People in a desperate situation will do what they can to get food for their loved ones.”

Survivor Michel Legros, 53 – awaiting help to search for seven relatives in the rubble of his collapsed home – said plaintively: “They’re scavenging everything. But what can you do?”

And aid worker Fevil Dubien told how people almost came to blows as he distributed water from a truck.

The grim scenes came as the first Brit confirmed missing was named as UN worker Ann Barnes, 59, of Leigh-on-Sea, Essex. She is feared trapped in the ruins of the organisation’s HQ.

Anxious sister Irene Marquet said: “At the time of the quake she was on the second floor of the main building. She must still be in the rubble, which is an awful thing to know.

“I believe everything is being done but it’s desperate. There’s been no trace, which is horrendous. One wants to remain hopeful but it gets more and more difficult.”

But there was joy for Daphnee Plaisin and Reginald Claude as rescuers pulled out their two-year-old son Redjeson Hausteen unharmed after almost three days trapped under rubble.

Fears for law and order in Port-au-Prince have been made worse by 4,000 inmates fleeing its destroyed main jail.

International Red Cross spokesman Marcal Izard said: “They obviously took advantage of this disaster.” More than 300 American soldiers arrived at the Port-au-Prince airport on Thursday night as the

US aims to have 8,000 troops in the country within days.

Others arrived at the capital’s harbour on the aircraft carrier USS Carl Vinson.

Lt Gen Ken Keen said: “We’ve much more support on the way. Our priority is getting relief out to needy people.” The White House made clear they would also beef up security to stop Haiti sliding into anarchy.

Helicopters have been ferrying water and other supplies from the ship to the airport.

But by yesterday morning there was still no sign of help reaching the streets of downtown Port-au-Prince other than a US Navy helicopter overhead. Kim Bolduc, acting head of the United Nations’ WFP arm, said the “risk of social unrest very soon” made it crucial to hand out aid quickly.

Sylvain Angerlotte, 22, spoke for millions of his countrymen and women as he said starkly: “We need food. People are suffering. My neighbours and friends are suffering. We don’t have money. We don’t have nothing to eat. We need pure water.”

But Ms Casella highlighted the difficulties caused by the quake’s devastation as she said: “The physical destruction is so great that physically getting from point A to B with supplies is not an easy task.”

Nonetheless, the WFP began setting up food and water distribution centres on Thursday. It plans to start handing out 6,000 tons of food in the capital’s rundown Cite Soleil district and is preparing shipments of enough ready-to-eat meals to feed two million Haitians for a month.

Up to 50,000 people are feared dead after the 7.0-magnitude quake.

Haitian President Rene Preval said government crews spent 20 hours removing 7,000 corpses from streets and morgues and burying them in mass graves.

But yesterday hundreds of bodies remained stacked outside the city’s main morgue. Thousands more are believed trapped under ruins.

There are fears the decaying corpses could trigger epidemics. Action Aid’s Haiti director Jean-Claude Fignole, said: “There are bodies everywhere. Hundreds of thousands of survivors are living in close proximity to the dead. The potential for sickness and disease is staggering.”

Aid worker Liony Batista added: “I don’t think that a word has been invented for what is happening in Haiti. It is total disaster.” The world has so far pledged some £240million in aid – a quarter of it from the United States.